How to hide EFI-partition?

Apparently, it wasn't the EFI- but recovery-partition, which showed up due to a bug being present in the upgrade to v1803 of Windows 10.

Following simple line did hide it in an administrator command prompt: mountvol e: /d where e: is to be replaced by it designated drive letter. Disk Management didn't offer any such option due to the partition being essential for the system.

Following the instructions of user Japelo_1976 in this thread helped me.

You have to delete the registry file with regedit for the volume you want to remove the drive letter.

1. Open Windows Powershell or the command line as administrator:
   Start→Right click Powershell→Run as administrator

2. Open diskpart:
   diskpart

3. Identify the EFI partition showing up in Explorer:
   list volume

4. Select the EFI partition (replacing the X with the correct drive letter):
   select volume X

5. Remove the EFI partition's drive letter (replacing the X with the correct drive letter):
   remove letter=X

6. Exit diskpart:
   exit

7. Open regedit:
   Start→Type regedit

8. Find the right key/folder:
   Computer\HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices

9. If the EFI partitions drive letter is still in the registry, delete the value:
   e.g. \DosDevices\X:

10. Close RegEdit and reboot.

It is normal for EFI partition to show up in Disk Management. But it shouldn't show up in This PC. You can, however, remove its drive letter so that it is hidden from This PC.

To do this:

1. Open Disk Management
2. Right-click on the partition
3. Select "Change Drive Letter and Paths..."
4. Click "Remove"
5. Click OK

You can do this with diskpart too.

1. Run diskpart.
2. Enter list volume and press Enter.
3. Find the volume you'd like to hide and memorize its number.
4. Enter select volume [number] where [number] is the number you memorized.
5. Enter remove and press Enter.